1. Technical Field
The present invention relates in general to and, in particular, to an improved system, method, and apparatus for improving the pinning strength of anti-parallel (AP) pinned giant magnetoresistive (GMR) and tunneling magnetoresistive (TMR) sensors using extra thin, ruthenium (Ru) alloy spacers that are annealed in a high magnetic field.
2. Description of the Related Art
A spin valve type giant magnetoresistive thin film used for a magnetic recording head of a hard disk drive has a multilayer film structure comprised of a plurality of layers or thin films. These layers include an antiferromagnetic layer, a fixed magnetization layer, a nonmagnetic conductive layer, and a free magnetization layer. In the multilayer film structure of the spin valve type giant magnetoresistive thin film, the nonmagnetic conductive layer is formed between the fixed magnetization layer and the free magnetization layer so that the two are isolated by the nonmagnetic conductive layer. Further, since the antiferromagnetic layer is made to adjoin the fixed magnetization layer, the magnetic moment of the fixed magnetization layer is fixed in one direction by the exchange coupling with the antiferromagnetic layer. On the other hand, the magnetic moment of the free magnetization layer is freely rotated in accordance with the external magnetic field.
The spin valve type giant magnetoresistive thin film generates the so-called “giant magnetoresistive effect,” or the change of the electrical resistance due to the relative angle formed by the magnetic moment of the fixed magnetization layer and the magnetic moment of the free magnetization layer. The rate of change of the electrical resistance due to the giant magnetoresistive effect is called the “magnetoresistive ratio” (MR ratio). The MR ratio of a spin valve type giant magnetoresistive thin film is far higher than that of a conventional anisotropic magnetoresistive thin film.
There are three types of spin valve type giant magnetoresistive thin films. The first type is known as a “bottom type” and comprises, from a substrate side, a buffer layer, an antiferromagnetic layer, a fixed magnetization layer, a nonmagnetic conductive layer, a free magnetization layer, and a protective layer that are stacked in that order. The second type is known as a “top type” and comprises a substrate, a buffer layer, a free magnetization layer, a nonmagnetic conductive layer, a fixed magnetization layer, an antiferromagnetic layer, and a protective layer in that order. The third type is called a “dual type” and comprises a substrate, a buffer layer, a first antiferromagnetic layer, a first fixed magnetization layer, a first nonmagnetic conductive layer, a free magnetization layer, a second nonmagnetic conductive layer, a second fixed magnetization layer, a second antiferromagnetic layer, and a protective layer in that order.
There have been proposed thin films for replacing the single layers of the fixed magnetization layers with synthetic ferromagnetic structures having fixed magnetization layer elements, nonmagnetic layers, and fixed magnetization layer elements. Furthermore, the free magnetization layer also comes in single layer structures and multilayer structures. In free magnetization layers and fixed magnetization layers of multilayer structures, all the layers are magnetic films, but sometimes different magnetic films are stacked or a sandwich structure interposing a nonmagnetic film therebetween is used.
The giant magnetoresistive effect of spin valve type giant magnetoresistive thin film is due to spin-dependent scattering of conductive electrons at the stacked interfaces of multilayer films. Therefore, to obtain a high MR ratio, cleanliness or flatness of the interfaces becomes important in the process of production of the spin valve film. Therefore, in the spin valve type giant magnetoresistive thin film, to achieve the cleanliness or flatness of the interfaces, the films are often formed continuously in the same vacuum chamber so that the intervals between formations of one layer and another become as short as possible.
Techniques for forming a film in vacuum include magnetron sputtering, ion beam sputtering, electron cyclotron resonance (ECR) sputtering, facing target sputtering, high frequency sputtering, electron beam evaporation, resistance heating evaporation, molecular beam epitaxy (MBE), etc.
To obtain a high MR ratio, the thickness of the nonmagnetic conductive layer should be small so as to suppress the flow of conductive electrons not contributing to the giant magnetoresistive effect (shunt effect). If the thickness of the nonmagnetic conductive layer is made small, however, the fixed magnetization layer and the free magnetization layer will end up coupling ferromagnetically through the nonmagnetic conductive layer. The interlayer coupling magnetic field between the fixed magnetization layer and the free magnetization layer should be small for practical use of the magnetic recording head of a hard disk drive. In the past, to reduce the interlayer coupling magnetic field, the thickness of the nonmagnetic conductive layer was set to 2.5 to 3.5 nm.
The technique of reducing the ferromagnetic coupling occurring between the fixed magnetization layer and the free magnetization layer by inserting a nano oxide layer of a size of not more than 1 nm into the fixed magnetization layer in the bottom type of spin valve film has been proposed. As a result, a relatively small interlayer coupling magnetic field is obtained and a high MR ratio is obtained even with a thin (2.0 to 2.5 nm) nonmagnetic conductive layer. That is, in the conventional spin valve type giant magnetoresistive thin film, the thickness of the nonmagnetic conductive layer was set thick (2.5 to 3.5 nm) to reduce the interlayer coupling magnetic field, but the problem arose of a flow of conductive electrons not contributing to the giant magnetoresistive effect (shunt effect) and the MR ratio ending up being reduced. Further, in the process of production of the above nano oxide layer, an oxidation step becomes necessary in the middle of formation of the fixed magnetization layer. An oxidation step is complicated and is poor in reproducibility. Thus, an improved solution would be desirable.